Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “CASEIN”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 973 records · Page 54Linked to original sources
PubMed1981

Kinetics of aggregation of alpha s1-casein/Ca2+ mixtures: charge and temperature effects.

Time-dependent light-scattering studies have been made on mixtures of alpha s1-casein and Ca2+, at fixed temperature over a range of [Ca2+] and [alpha s1-casein], and also as functions of temperature. Measurements were also made of the extent of precipitate formation in the casein/Ca2+ mixtures, using centrifugation. The results are analysed in terms of a monomer-octamer equilibrium between calcium caseinate particles followed by a Smoluchowski aggregation in which only the octamers can participate. The equilibrium constant is dependent upon the charge on the protein/Ca2+ particles, and hence can be related to the extent of binding of Ca2+ to the alpha s1-casein. The Smoluchowski constant is likewise shown to be charge-dependent. The variation of the reaction rate with temperature can be ascribed solely to the changing charge of the alpha s1-casein/Ca2+ complex caused by changed binding of Ca2+ at different temperatures.

Animals↗
PubMed1981

Some association properties of bovine SH-kappa-casein.

(1) It is shown that kappa-casein association is characterized by a critical micelle concentration which decreases as the ionic strength is increased. (2) The kappa-casein polymer molecular weight was calculated from the weight-average apparent molecular weight by taking into consideration the monomer concentration and the excluded volume. The degree of polymerization is 30 and does not depend on ionic strength between 0.1 and 1 M. (3) The non-electrical contribution to the standard free energy of association is -38 kJ/mol monomer. The electrical part is small: 1-2 kJ/mol monomer depending on the ionic strength and kappa-casein genetic variant. (4) The limitation of size and the size itself of the kappa-casein polymer can be explained by the theory of self-assembly of virus particles by Caspar and Klug (D.L.D. Caspar and A. Klug, Cold Spring Harb. Symp. Quant. Biol. 27 (1962)1). (5) Extending this theory to casein micelle assembly, it is predicted that micelles are distributed preferentially over a restricted number of sizes.

Animals↗
PubMed1990

Osmotic shock of cultured primary mammary cells amplifies the hormonal induction of casein gene expression.

Primary cells from rabbit mammary gland cultured on floating collagen were transfected with various plasmids in different conditions. Conventional transfection methods using DEAE-dextran or calcium phosphate followed by an osmotic shock with dimethyl sulphoxide (DMSO), polyethylene glycol (PEG) or glycerol did not prevent lactogenic hormones to induce casein synthesis. On the contrary and unexpectedly, casein synthesis was markedly stimulated by transfection. This amplification was obtained as well with DMSO, PEG and glycerol alone or in the presence of DEAE-dextran, calcium phosphate or DNA. None of these compounds induced casein synthesis in the absence of prolactin. A shock by DMSO also amplified the accumulation of beta-casein mRNA in the presence of prolactin. These results show for the first time that primary cultured mammary cells can be efficiently transfected and still keep their capacity to respond to lactogenic hormones. They also indicate that the short osmotic shocks conventionally used in transfection have a potent long-term stimulatory effect on casein gene expression, which is mediated through an unknown mechanism.

Animals↗
PubMed1977

Rat casein: isolation and characterization of two major fractions.

1. In rat milk, casein exists as particles of 77 nm mean diameter, similar in appearance to the casein micelles in the milk of other species. 2. The heterogeneity of rat casein was investigated by polyacrylamide gel electrophoresis and by chromatography on DEAE-cellulose, both in the presence of 8 M-urea. 3. The chromatography yielded two fractions, D2 and D4. 4. In chemical composition, D2 resembles the kappa-caseins of other species, while D4 resembles the alpha 5-caseins of other species. 5. D2 is soluble in 80 mM-CaCl2 at 37 degrees C, but D4 is insoluble under these conditions. 6. In 80 mM-CaCl2 at 37 degrees C, D2 prevents the precipitation of D4 by the formation of particles similar to those found in rat milk.

Animals↗
PubMed1988

Characterization of proteins and fatty acid composition in Galapagos fur seal milk. Occurrence of whey and casein protein polymorphisms.

1. Milk proteins of the Galapagos fur seal (Arctocephalus galapagoensis) were separated adequately into whey and casein fractions using bovine milk analysis methods. 2. In samples from days 5-30 of lactation 40% of the total proteins were whey and 60% caseins; in mid-lactation, day 150, 25% were whey and 75% casein proteins. 3. Electrophoretic and isoelectric focusing patterns of fur seal whey protein differed widely from bovine patterns, whereas those of caseins were similar. 4. Polymorphisms of fur seal whey and casein proteins were noted and did not seem related to different stages of lactation. 5. C-16 and C-18 fatty acids contributed about 70% of fatty acids; 63% of the total acids in milk fat were unsaturated.

Animals↗
PubMed1995

Human alpha s1-casein: purification and characterization.

The human counterpart of alpha s1-casein has been purified by a combination of gel-filtration and ion-exchange chromatography under denaturing conditions. SDS-PAGE analysis revealed the presence of a diffuse ladder with a high molecular mass which upon reduction was replaced by several closely spaced bands of lower molecular masses and a broad diffuse band corresponding to kappa-casein. Amino acid sequence analysis of the closely spaced bands all resulted in the same N-terminal sequence which was found to be homologous with alpha s1-casein from other species. Sequence analysis of a major radiolabelled tryptic peptide from purified 14C-carboxymethylated alpha s1-casein demonstrated that the protein contains at least two cysteine residues. As judged by SDS-PAGE in the presence or absence of a reducing agent, the molecular structure of the polymers constituting the ladder is composed of heteropolymers of alpha s1- and kappa-casein cross-linked by disulfide bonds.

Amino Acid Sequence↗
PubMed2005

Chemical synthesis and structure elucidation of bovine kappa-casein (1-44).

The caseins (alphas1, alphas2, beta, and kappa) are phosphoproteins present in bovine milk that have been studied for over a century and whose structures remain obscure. Here we describe the chemical synthesis and structure elucidation of the N-terminal segment (1-44) of bovine kappa-casein, the protein which maintains the micellar structure of the caseins. kappa-Casein (1-44) was synthesised by highly optimised Boc solid-phase peptide chemistry and characterised by mass spectrometry. Structure elucidation was carried out by circular dichroism and nuclear magnetic resonance spectroscopy. CD analysis demonstrated that the segment was ill defined in aqueous medium but in 30% trifluoroethanol it exhibited considerable helical structure. Further, NMR analysis showed the presence of a helical segment containing 26 residues which extends from Pro8 to Arg34. This is the first report which demonstrates extensive secondary structure within the casein class of proteins.

Amino Acid Sequence↗
PubMed2005

Role of xanthine oxidase, lactoperoxidase, and NO in the innate immune system of mammary secretion during active involution in dairy cows: manipulation with casein hydrolyzates.

The aims of this study were to test whether xanthine oxidase, lactoperoxidase, and NO are components of the innate immune system of mammary secretion during active involution in dairy cows, and whether the innate immune system is activated by casein hydrolysates. Our laboratory has shown recently that infusion of CNH into mammary glands induced involution and was associated with earlier increases in the concentrations of components of the innate immune system. Intact casein is inactive and served as control. Half of the glands of 8 Holstein cows scheduled for dry off (approximately 60 days before parturition) were injected for 3 days with a single dose of casein hydrolyzates and the contralateral glands with a single dose of intact casein with the same concentration. Involution elicited marked increases in xanthine oxidase and lactoperoxidase activities, and accumulation of urate and nitrate. NO and H(2)O(2) were constantly produced in the mammary gland secretion. Nitrite formed either by autooxidation of NO or by conversion of nitrate to nitrite by xanthine oxidase was converted into the powerful nitric dioxide radical by lactoperoxidase and H(2)O(2) that is derived from the metabolism of xanthine oxidase. Nitric dioxide is most likely responsible for the formation of nitrosothiols on thiol-bearing groups, which allows an extended NO presence in mammary secretion. Nitrite is effectively converted to nitrate, which accumulated in the range of approximately 25 microM -1 mM from the start of the experiment to the complete involution of glands. The mammary secretion in all glands was bactericidal and bacteriostatic during established involution, and this appeared sooner and more acutely in glands treated with casein hydrolyzates, within 8 to 24 h. It is concluded that xanthine oxidase, lactoperoxidase, and NO are components of the mammary innate immune system that form bactericidal and bacteriostatic activities in mammary secretions. The innate immune system play a major role in preventing intramammary infection during milk stasis and its activation may increase its effectiveness.

Animals↗
PubMed1996

Nuclear magnetic resonance study of the conformation and dynamics of beta-casein at the oil/water interface in emulsions.

A (13)C and (31)P nuclear magnetic resonance (NMR) study has been carried out on beta-casein adsorbed at the interface of a tetradecane/water emulsion. (13)C NMR spectra show signals from the carbonyl, carboxyl, aromatic, and C alpha carbons in beta-casein, well resolved from solvent resonances. Only a small fraction of all carbon atoms in beta-casein contribute to detectable signals; intensity measurements show that the observable spectrum is derived from about 30 to 40 amino acid residues.(31)P NMR spectra show signals from the five phosphoserines on the hydrophilic N-terminal part of the protein. Analysis of T(1) relaxation times of these nuclei, using the model free approach for the spectral density function and the line shape of the alpha-carbon region, indicates that a large part of the protein is in a random coil conformation with restricted motion and a relatively long internal correlation time. The NMR results show that the conformation and dynamics of the N-terminal part of beta-casein are not strongly altered at the oil/water interface, as compared to beta-casein in micelle-like aggregates in aqueous solution.

Adsorption↗
PubMed1998

Preparation of casein-chitosan microspheres containing diltiazem hydrochloride by an aqueous coacervation technique.

Sustained release casein-chitosan microspheres containing diltiazem hydrochloride (DTZ) were prepared with colloidal coacervation technique in a completely aqueous environment. The interaction between chitosan solution in dilute acetic acid (5% v/v) and casein solution in 0.5 M sodium hydroxide was the basis for the microspheres formation. Formaldehyde was used for the surface hardening of the droplets by cross-linking and thus fixing the shape and surface morphology of the formed microspheres. The entrapment efficiencies of the microspheres were variables (14.5-53.7%) depending on the preparation conditions. The prepared microspheres exhibited an angle of repose values between 31.9-42.0 degrees indicating good free flowing nature, whereas DTZ powder as such was non-flowable. The dissolution profiles of DTZ from casein-chitosan microspheres showed retarded release pattern of the drug into distilled water. Casein and chitosan concentrations, initial drug concentration and stirring time were found to be the main parameters that affect the properties and the performance of the prepared microspheres. The retarded release of DTZ was increased by increasing casein concentration, and stirring time. On the other hand, increasing chitosan concentration and using high initial drug loading showed a fast drug release.

Animals↗
PubMed2002

Dynamic light scattering investigation of sodium caseinate and xanthan mixtures.

Aqueous solutions of sodium caseinate and xanthan at pH 7 and containing 0.1 M NaCl, and their mixtures were investigated using dynamic light scattering. Sodium caseinate solutions showed a bimodal distribution of relaxation rates; with the aggregate peak distribution predominating. Xanthan solutions showed a single distribution at low concentrations (< or =0.06 wt.%) and a bimodal distribution at higher concentrations. The sodium caseinate-xanthan mixture modes were independent of the total biopolymer concentration, and behaved as a superposition of sodium caseinate solution alone and xanthan solution alone. This indicates that there is no interaction between xanthan and sodium caseinate in the range of concentrations considered in this study.

Caseins↗
PubMed1985

Complete sequence of ovine alpha s2-casein messenger RNA.

The primary structure of mRNA coding for ovine alpha s2 casein has been determined by chemical sequencing of three cDNA clones and the primer extension products of the longest one. The mRNA was 1,024 nucleotides long, excluding the poly(A) tail. The length of the 5' noncoding, coding and 3' noncoding regions was 53, 669 and 302 nucleotides, respectively. A comparison of the nucleotide sequence of ovine alpha s2-casein and guinea-pig casein A mRNAs revealed an extensive homology in the 5' and 3' noncoding regions. The deduced amino acid sequence of ovine alpha s2-casein was compared with its bovine and guinea-pig counterparts. Moreover, an heterogeneity was evidenced in the mRNA population of the alpha s2-casein.

Amino Acid Sequence↗
PubMed1998

Casein secretion in mammary tissue: tonic regulation of basal secretion by protein kinase A.

Despite its quantitative importance in the secretion of lactoproteins, little is known about the triggering and control mechanisms that initiate, regulate and terminate the operation of the basal pathway of lactoprotein secretion throughout the lactation cycle. This study investigated the possible modulation by cAMP-mediated mechanisms, of cellular transit of newly-synthesised caseins and their basal secretion in explants of mammary tissue from lactating rats and rabbits. Enhancement of the rate of secretion of newly-synthesised caseins occurs when mammary explants are challenged in vitro with agents that activate protein kinase A (PKA). Inhibition of PKA slows casein secretion. The PKA-sensitive step(s) in casein secretion is early in the exocytosis pathway but inhibition of PKA does not impair casein maturation. Ultrastructural, immunochemical and biochemical methods locate PKA on membranes of vesicles situated in the Golgi region. Exposure of tissue to a cell-permeant PKA inhibitor results in morphological modification of these vesicular structures. We conclude that PKA mediates tonic positive regulation of the basal secretory pathway for lactoproteins in the mammary epithelial cell.

Animals↗
PubMed1998

A distal enhancer region in the human beta-casein gene mediates the response to prolactin and glucocorticoid hormones.

The 5' flanking region of the human beta-casein gene was investigated for the presence of regulatory sequences mediating the action of the lactogenic hormones prolactin and dexamethasone. DNA encompassing 9389 base pairs of the flanking region was isolated and a sequence comparison performed with regulatory regions previously identified in the beta-casein gene of rodents and ruminants. The analysis revealed the presence of a distal region between -4700 and -4550 with a high percentage of identity to the bovine beta-casein enhancer region, and a proximal region between -1 and -200 similar to the proximal promoter regions found in rodents and ruminants. Reporter gene constructs under the control of the distal or the proximal region of the human beta-casein gene were tested for their responsiveness to prolactin and dexamethasone. In transfection experiments, the distal region functioned as a lactogenic hormone inducible enhancer, whereas the proximal region exhibited low activity. In electromobility shift assays, multiple binding sites for Stat5, CCAAT/enhancer-binding proteins, and Ets domain proteins were identified in the distal human enhancer. These transcription factors have already been demonstrated as important regulators of the transcription of milk protein genes in rodents. Thus, a common set of transcription factors appears to be required for the expression of the human beta-casein gene and of milk protein genes in other species.

Animals↗
PubMed1997

Oxidation of bovine beta-casein by hypochlorite.

We recently observed two 2,4-dinitrophenylhydrazine (DNPH)-reactive proteins of 40 and 120 kDa in the bronchoalveolar lavage fluids of rats exposed to >95% O(2) for 48 h. The N-terminal sequences of these proteins were both identical over 16 amino acids with rat beta-casein, which, in addition to its more common association with milk, is produced by cytotoxic T-lymphocytes, and has been found to have proinflammatory properties. Because of the inflammatory response that accompanies hyperoxic lung injury, we investigated the oxidation of bovine beta-casein by HOCl. Following exposure to HOCl at 4 degrees C for 15 min, derivatization with DNPH, washing, and digestion with trypsin, the resultant peptides were separated by reverse-phase HPLC. One peptide isolated from a peak absorbing at 365 nm was identified as AVP(Y*)PQR, corresponding to amino acids 177-183 of bovine beta-casein. Analysis of the peptide by both electrospray and matrix assisted laser desorption ionization (MALDI) mass spectrometry identified a molecular ion MH+ of 1008.5 Da, which represents an increase of 178 Da from the calculated monoisotopic MH+ of the unmodified peptide of 830.45 Da. Daughter ion spectra of the doubly charged parent ion of the peptide further support the oxidation of the tyrosine to the quinone methide, with subsequent conversion to the corresponding hydrazone with DNPH. A second pair of products were identified as arising from oxidation of Y(193) within the tryptic peptide constituted by amino acids 184-202, and the corresponding chymotryptic cleavage side product, 191-202. Exposure of beta-casein to increasing amounts of HOCl revealed that M and Y residues were the most susceptible, although bovine beta-casein contains no C, and a single W, which would not be detected by our methods. The approach described in the present report can be used to evaluate the contributions of distinct mechanisms of oxidation in other experimental or pathological models.

Amino Acid Sequence↗
PubMed1992

Brain casein kinase 2: affinity purification procedure using immobilized polyethylenimine.

A simplified procedure for casein kinase 2 purification from bovine brain is described. The purification procedure consists of two affinity chromatography steps, using heparin and polyethylenimine immobilized on a synthetic matrix (Toyopearl 650M). The adsorption and elution conditions for each column were optimized, resulting in a simple elution protocol for each column. A stable, highly purified casein kinase 2 preparation was obtained in 4 h using this procedure. Polyethylenimine was shown to stimulate the casein kinase 2 activity using exogeneous substrates (casein, calmodulin, MAP2, and tau) but not the enzyme's autophosphorylation activity. The polyethylenimine stimulation could be overcome by applying a mass excess of the casein kinase 2 inhibitor, heparin.

Animals↗
PubMed2000

Capillary electrophoresis characterization of the casein fraction of cheeses made from cows', ewes' and goats' milks.

Casein fractions and their breakdown products in Iberico-type cheeses made from the milk of cows, ewes or goats were analysed by capillary electrophoresis in order to characterize them. The actions of plasmin and chymosin on caseins were evaluated by comparing the electropherograms of caseins from milk and from cheese, both with and without treatment with plasmin. Characteristic capillary electrophoresis patterns were obtained for cheeses made from the milk of each of the three species, and the main components were identified. Caprine para-kappa-casein and bovine beta-caseins, eluting at the first and at the last part of the electropherogram respectively, were found to be indicative of the presence of the milks of these species.

Animals↗
PubMed2000

Accumulation of casein-derived peptides during growth of proteinase-positive strains of Lactococcus lactis in milk: their contribution to subsequent bacterial growth is impaired by their internal transport.

To explain the limited nutritional value of milk cultured with proteinase-positive (Prt+) strains of Lactococcus lactis for the subsequent growth of dairy lactococci, we investigated further the time courses of modifications in the free amino acid and peptide contents of cultured milk. When growing in milk for up to 24 h, Prt+ strains of Lc. lactis progressively accumulated amino acids and casein-derived peptides. The growth of proteinase-negative (Prt-) wild-type strains and peptide transport mutants of Lc. lactis in cultured milk showed that casein-derived peptides could sustain growth up to 5 x 10(8) cfu/ml, depending on the extent of casein degradation during the preliminary growth of Prt+ strains and the Prt- strains. Of the casein-derived oligopeptides, < 25% were transported into the cell and used for Lc. lactis growth. However, they played a prominent role, contributing 90% to growth. In contrast, di- and tripeptides did not contribute to growth, suggesting that either few were released from caseins or they did not supply essential amino acids.

Amino Acids↗